Tuning the emission of cationic iridium (III) complexes towards the red through methoxy substitution of the cyclometalating ligand
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The synthesis, characterization and evaluation in solid-state devices of a series of 8 cationic iridium complexes bearing different numbers of methoxy groups on the cyclometallating ligands are reported. The optoelectronic characterization showed a dramatic red shift in the absorption and the emission and a reduction of the electrochemical gap of the complexes when a methoxy group is introduced para to the Ir-C bond. The addition of a second or third methoxy group does not lead to a significant further red shift in these spectra. Emission maxima over the series ranged from 595 to 730 nm. All complexes possessing a motif with a methoxy group at the 3-position of the cyclometalating ligands show very short emission lifetimes and poor photoluminescence quantum yields whereas complexes having a methoxy group at the 4-position are slightly blue shifted compared to the unsubstituted parent complexes, resulting from the inductively electron withdrawing nature of this directing group on the Ir-C bond. Light-emitting electrochemical cells were fabricated and evaluated. These deep red emitters generally show poor performance with electroluminescence mirroring photoluminescence. DFT calculations accurately model the observed photophysical and electrochemical behavior of the complexes and point to an emission from a mixed charge transfer state.
Hasan , K , Bansal , A K , Samuel , I D W , Roldán-Carmona , C , Bolink , H & Zysman-Colman , E 2015 , ' Tuning the emission of cationic iridium (III) complexes towards the red through methoxy substitution of the cyclometalating ligand ' Scientific Reports , vol 5 . DOI: 10.1038/srep12325
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EZ-C acknowledges CFI (Canadian Foundation for Innovation), NSERC (the Natural Sciences and Engineering Research Council of Canada), FQRNT (Le Fonds québécois de la recherche sur la nature et les technologies) and the University of St Andrews for financial support. C. R-C. would like to thank the MINECO for the financial support of this research in the framework of project CTQ2010-17481, the Junta de Andalucía (CICyE) for special financial support (P08-FQM-4011 and P10-FQM-6703) and the MECD (Spanish Ministry of Education, Culture, and Sport) for an FPU grant. This work has been supported by the Spanish Ministry of Economy and Competitiveness (MINECO) (MAT2014-55200), the Generalitat Valenciana (Prometeo/2012/053). IDWS and AKB acknowledge financial support from the EPSRC of the UK (grant: EP/J01771).